code: def test_big_m_formulation_block():
      onnx_model = onnx.load(
          Path(__file__).parent / "continuous_model.onnx"
      )
      model = GradientBoostedTreeModel(onnx_model)
  
      m = pe.ConcreteModel()
      m.mod = OmltBlock()
      formulation = GBTBigMFormulation(model)
      m.mod.build_formulation(formulation)
  
      m.obj = pe.Objective(expr=0)
  
file_path: OMLT/tests/gbt/test_gbt_formulation.py
imports: from pathlib import Path
  import pyomo.environ
  import pytest
  from omlt import OmltBlock
  from omlt.dependencies import onnx, onnx_available
  from omlt.gbt.gbt_formulation import GBTBigMFormulation
  from omlt.gbt.model import GradientBoostedTreeModel
label_desc: Use image node_id 2 for calling a global function with example usage: test_big_m_formulation_block() without return types